DESCRIPTION
ARC WELDING METHOD AND ARC WELDING APPARATUS
TECHNICAL FIELD
The present invention relates to an arc welding method and an arc
welding apparatus of consumable electrode type used for welding by
generating arc between a welding wire serving as a consumable electrode
and a base metal as an object to be welded while feeding the welding wire.
BACKGROUND ART
There is a rising demand in recent years in the welder industry for
improvement of arc-starting performance in order to increase the
productivity by shortening welding time and to obtain high quality in the
welding result. One of the methods of shortening the welding time is to
reduce a processing time to end the welding. Also useful is to optimize a
shape of the tip of the wire at the end of welding, as one of the methods of
improving the arc-starting performance. The both methods pertain to
control process at the end of the welding.
Fig. 4 is a schematic diagram showing a general structure of a
conventional arc welding apparatus. Primary rectifier element 3 rectifies
the power input from mains power source 1. Switching element 4 switches
an output of primary rectifier element 3 to produce an output suitable for
welding. Main power transformer 2 converts the output of switching
element 4 into an output suitable for welding. Secondary rectifier element
6 rectifies the output of main power transformer 2. Reactor 5 smoothes the
output of secondary rectifier element 6 into a current form suitable for
welding. Welding current detector 8 detects a welding current. Welding
voltage detector 9 detects a welding voltage. Short/arc detector 10
determines whether welding condition is in a short mode, in which wire 16
and base metal 15 are in contact with and stay shorted, or in an arcing
mode, in which they have opened out of the short mode and arc is being
generated, according to a welding voltage detector signal. Welding start
dictator 35 inputs a welding start signal and a welding end signal to
welding power unit 14 from the outside. Welding-end determining section
34 determines an end point of the welding time based on the input from
welding start dictator 35. Integrator section 30 computes an integrated
amount of welding current, starting from a time immediately after opening
of the shorting at the end of welding portion. Threshold value setting
section 31 sets a threshold value for comparison with the integrated
amount of welding current. Comparator section 32 compares the
integrated amount of welding current with the threshold value. Output
controller 36 outputs a signal for controlling welding power output. Driver
33 outputs a signal for driving switching element 4 to control the welding
power output.
Welding voltage detector 9 is connected across output terminals of
welding power unit 14, and outputs a signal corresponding to a detected
voltage. Short/arc detector 10 judges based on the signal from welding
voltage detector 9 as to whether the welding power output voltage is at
least equal to or less than a predetermined value. Using a result of this
judgment, short/arc detector 10 determines whether wire 16 is in a short
mode by being in contact and shorted with base metal 15 of the object to be
welded, or an arcing mode by being not in contact with base metal 15, and it
then outputs a determination signal.
Fig. 5 is a graphic representation illustrating waveforms of wire
feeding speed Wf, welding voltage Vw and welding current Aw in the
conventional method of arc welding.
Referring now to Fig, 4 and Fig, 5, description is provided of the
conventional method of controlling the arc welding. When a welding end
signal is input from welding start dictator 35 at time Tl, welding-end
determining section 34 detects a point of time from which to start
controlling the end of welding. The wire feeding speed is then decelerated
at a predetermined inclination toward a stop. When a change occurs in the
detection from the short mode to the arc mode, short/arc detector 10
determines this point as to be time T2 for a globule on the tip end of wire 16
to move to base metal 15. Taking time T2 as a starting point, integrator
section 30 starts integrating output current to obtain an integrated value,
and comparator section 32 compares this integrated value with the
threshold value set by threshold value setting section 31. When the
integrated value reaches the threshold value, the output current of a
predetermined value set beforehand by output controller 36 is supplied for
a predetermined time period tl to form a globule at the tip end of wire 16,
and the welding power output is terminated (refer to patent literature
PTL1 for instance).
It becomes possible by the above method to control a shape of the tip
end of the wire to have a uniform size without variations at the end of
welding, and limit the influence of slag upon starting the subsequent arc,
thereby achieving an excellent arc-starting performance.
According to the conventional method of welding control discussed
above, it is possible to control the shape of tip end of the wire to be uniform
in size without variations. However, when attempted to control and form a
globule of a small size (e.g., about 1.1 to 1.3 times the diameter of the wire)
on the tip end of wire 16, there are cases wherein a stick or the globule is
absorbed into a molten metal pool due to heaving and the like of the molten
metal pool, resulting in a failure to form the globule of desired size.
CITATION LIST
Patent Literature:
PTL l: Unexamined Japanese Patent Publication No. 2002-292464
SUMMARY OF THE INVENTION
An arc welding method of the present invention comprises the steps of
accelerating a feeding speed of a welding wire to cause shorting between
the welding wire and a base metal when a welding end signal is input
during a period of arcing, retracting the welding wire backward thereafter
until a wire retracting speed reaches a predetermined rate, controlling the
wire retracting speed to maintain it constant for a predetermined duration
of time, then stopping the backward retraction of the welding wire, and
then terminating a welding power output after supplying a predetermined
amount of welding current for a predetermined duration of welding time
starting from a point of time when opening of the shorting occurs during the
backward retraction of the welding wire.
A result of this is to achieve formation of a shape of the tip end of the
wire into an optimum size without variations and to obtain a globule of the
desired size appropriate for improving arc-starting performance.
BRIEF DESCRIPTION OF DRAWINGS
Fig. 1 is a schematic diagram showing a general structure of an arc
welding apparatus according to a first exemplary embodiment of the
present invention;
Fig. 2 is a graphic representation illustrating waveforms of wire
feeding speed, welding voltage and welding current of the arc welding
apparatus;
Fig. 3 is another graphic representation illustrating waveforms of wire
feeding speed, welding voltage and welding current according to a second
exemplary embodiment of the present invention,'
Fig. 4 is a schematic diagram showing a general structure of a
conventional arc welding apparatus; and
Fig. 5 is a graphic representation illustrating waveforms of wire
feeding speed, welding voltage and welding current in a process of arc
welding with the conventional arc welding apparatus.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
Description is provided hereinafter of exemplary embodiments of the
present invention with reference to the accompanying drawings.
FIRST EXEMPLARY EMBODIMENT
Fig. 1 is a schematic diagram showing a general structure of an arc
welding apparatus according to the first exemplary embodiment of this
invention, and Fig. 2 is a graphic representation illustrating waveforms of
wire feeding speed, welding voltage and welding current of the arc welding
apparatus.
In Fig. 1, primary rectifier element 3 rectifies the power input from
mains power source 1. Switching element 4 regulates an output of primary
rectifier element 3 to produce an output suitable for welding. Main power
transformer 2 converts the output of switching element 4 into an output
suitable for welding. Secondary rectifier element 6 rectifies the output of
main power transformer 2. Reactor 5 smoothes the output of secondary
rectifier element 6 into a current form suitable for welding. Welding
current detector 8 detects a welding current. Welding voltage detector 9
detects a welding voltage. Short/arc detector 10 determines whether
welding condition is in a short mode, in which wire 16 and base metal 15
are in contact with and stay shorted, or in an arcing mode, in which they
have opened out of the short mode and arc is being generated, according to
a welding voltage detector signal output from welding voltage detector 9.
Here, wire 16 means a welding wire that serves as a consumable electrode,
and base metal 15 means an object to be welded.
Output controller 11 controls the welding power output. Welding start
dictator 12 gives a command of starting or stopping the welding power
output. Wire feeding speed controller 13 controls a wire feeding speed. Tip
20 is mounted to torch 18. Welding condition setting section 23 is used by
an operator to set welding conditions such as a welding current and a
welding voltage. In other words, output controller 11 controls switching
element 4 in a manner to produce any of predetermined current waveform
and voltage waveform according to a given electric current set in welding
condition setting section 23 and an output of short/arc detector 10.
Typical examples of welding start dictator 12 include a remote
controller connected to welding power unit 14 and a torch switch for torch
18. Other examples, in the case of using a welding robot, are a robotic
controller and the like having a program stored for operation of the robot.
Examples of welding condition setting section 23 include a remote
controller and the like connected to welding power unit 14. A robotic
controller having a stored operation program, a teaching pendant
connected with the robotic controller, and the like are also examples when a
welding robot is used.
Fig. 2 is a graphic representation illustrating waveforms showing
changes with time of wire feeding speed Wf, welding voltage Vw, or the
output voltage for welding, and welding current Aw, or the output current
for welding.
Time Tl shown in Fig. 2 is a time when a signal is input from welding
start dictator 12 for turning off the welding power output, and upon which a
control process is commenced for wire feeding speed Wf, welding current
Aw and welding voltage Vw in order to end the welding. Wire feeding speed
Wf is accelerated to predetermined amplitude and cycle (frequency), and
decelerated afterwards. A backward retracting; control of the wire is hence
carried out following the forward feeding control in a manner that, when a
backward retracting speed of the wire reaches a predetermined rate Wfl,
this retracting speed Wfl is maintained for a predetermined duration of
time t4, and the feeding/retracting speed is changed to 0, or it is stopped
upon a lapse of time t4. This forward feeding forcibly makes shorting, and
the subsequent backward retraction pulls up and separates wire 16 from
base metal 15 to forcibly open the shorting thereafter (time T6). Here,
predetermined wire retracting speed Wfl is roughly lm/min to 20m/min,
and predetermined retracting time t4 is roughly 10msec to 30msec.
Furthermore, predetermined amplitude of wire feeding speed Wf is roughly
2m/min to 25m/min, and a predetermined cycle is about 40 to 100 times per
second. In other words, the frequency is about 40Hz to 100Hz, which
correspond to a period of about 10msec to 25msec.
When the shorting is opened during the backward retraction, the tip
end of wire 16 becomes the smallest in shape without variations since it is
the moment immediately after a globule at the tip end of wire 16 is
absorbed in a molten metal pool. It is for this reason that a predetermined
value of constant welding current Al is output for a predetermined
duration of welding-current time t2 starting from time T6 to control the
shape of tip end of wire 16 to become the desired size. The predetermined
welding current Al necessary to melt wire 16 is approximately 30Ato 100A,
and the predetermined duration of welding-current time t2 is between
10msec and 30msec, for instance. These predetermined welding current Al
and predetermined duration of welding-current time t2 vary depending on
diameter and the like factors of wire 16. A distance between the tip end of
the wire and the base metal is set to be about 3mm to 8mm taking into
account a melted portion of wire 16 added to a distance being pulled back by
the backward retraction. Since the tip end of wire 16 is melted while it is in
the pulled-back position, a proper distance can be secured between the tip
end of the wire and the base metal even when forming the tip end of wire 16
into a small shape. This can prevent the tip end of wire 16 from coming in
contact with the molten metal pool and the globule from being absorbed in
the molten metal pool after the stick and the welding power output is
turned off.
In this first exemplary embodiment, the time to stop the wire feeding
speed is shown as not to coincide with the time to terminate the welding
power output, as such that the termination of the welding power output is
set later than the stop time of the wire feeding speed. However, they can be
set to coincide with each other, or the termination of the welding power
output may be set earlier than the other without problems, as their relation
becomes different depending on the diameter, etc. of wire 16.
Furthermore, in the first exemplary embodiment, the welding current
is reduced sharply within a short period of time (about 2msec) from opening
of the shorting at time T6 so as to ease controlling of the shape at the tip
end of wire 16. Accordingly, duration of predetermined welding-current
time t2 is timed beginning from time T6. -
Referring to Fig. 1 here, description is provided of an arc welding
apparatus of the consumable electrode type for carrying out arc-welding
control as discussed above. In Fig. 1, welding start dictator 12 sends a
welding end signal to output controller 11 and wire feeding speed controller
13 for turning off the welding power output. Wire feeding speed controller
13 accelerates the wire feeding speed according to the predetermined cycle
and amplitude, and decelerates thereafter. It then retracts wire 16
backward at predetermined retracting speed Wfl for the predetermined
duration of retracting time t4, and stops the retracting motion of wire 16.
Wire feeding speed controller 13 controls the wire feeding speed by
sending a signal for controlling the wire feeding speed to wire feeder 19. In
this instance, the waveform for changing the wire feeding speed may be of a
sinusoidal shape having predetermined cycle and amplitude as shown in
Fig. 2, or it can be changed to a waveform of trapezoidal shape.
Wire feeding speed controller 13 is provided with storage device 21 and
wire feeding speed decision section 22. Here, storage device 21 stores
relational formulas or a table (data chart), which coordinate such
parameters as a setting current, an average value of wire feeding speed, a
cyclic period (frequency) of the wire feeding speed, an amplitude of the wire
feeding speed, backward retraction time t4 and the like. Wire feeding speed
decision section 22 decides an average wire feeding speed, a frequency and
an amplitude of the wire feeding speed retrieved from storage device 21
based on the current set by welding condition setting section 23. Wire
feeding speed controller 13 receives outputs of short/arc detector 10 and
wire feeding speed decision section 22, and controls the wire feeding speed
by periodically repeating it forward and backward.
On the other hand, control of the welding power output given by the
welding current and welding voltage is carried out in the following manner.
Output controller 11 outputs a signal for controlling any of the welding
current and the welding voltage by using an appropriate parameter for a
shorting period, for instance if it is in the shorting period, corresponding to
the welding waveform parameter selected according to the welding current
and the welding voltage set by welding condition setting section 23. Or, it
outputs another signal for controlling any of the welding current and the
welding voltage by using an appropriate parameter for an arcing period if it
is in the arcing period. Any of these output signals is input to switching
element 4 to control the welding power output. When welding start dictator
12 inputs a welding end signal to output controller 11 for turning off the
welding operation, short/arc detector 10 outputs a signal of open-shorting
when the shorting is opened at time T6. Output controller 11 operates in a
manner to output a predetermined value of constant welding current Al for
a predetermined duration of welding-current time t.2 starting from time T6,
to control the size of the tip end of wire 16.
As discussed, the arc welding apparatus in the first exemplary
embodiment of the present invention is the consumable electrode type used
for welding by generating arc 17 between welding wire 16 serving as a
consumable electrode and base metal 15 as an object to be welded. The arc
welding apparatus comprises welding condition setting section 23,
switching element 4, welding voltage detector 9, welding start dictator 12,
short/arc detector 10, output controller 11, storage device 21, wire feeding
speed decision section 22 and wire feeding speed controller 13. Wire
feeding speed controller 13 of this arc welding apparatus accelerates wire
16 according to the predetermined cycle and amplitude to make shorting
between wire 16 and base metal 15 when a welding end signal is input
while arc 17 is being generated. It then retracts wire 16 backward
according to predetermined cycle and amplitude until the wire retracting
speed reaches a predetermined rate, and continues the backward retraction
thereafter by controlling the wire retracting speed constant at the
predetermined rate for a predetermined duration of time. After the
retracting motion of wire 16 is stopped, output controller 11 terminates the
welding power output after supplying the welding current of a
predetermined amount for a predetermined duration of welding time
starting from the point of time when opening of the shorting occurs during
the backward retraction of wire 16.
These operations can ensure a proper distance between the tip end of
the wire and the base metal even when the tip end of wire 16 has a small
shape so as to avoid sticking and prevent the tip end of wire 16 from coming
in contact with the molten metal pool after the termination of the welding
power output. Accordingly, it becomes possible to obtain the shape at the
tip end of wire 16 without variations, and the sufficient distance between
the tip end of wire 16 and the base metal 15 to prevent them from becoming
welded together, thereby avoiding interruption of the manufacturing
operation.
In the arc welding apparatus of the first exemplary embodiment of this
invention, the acceleration of wire 16 is carried out according to the
predetermined cycle and amplitude, and the backward retraction of
welding wire 16 is also carried out according to the predetermined cycle and
amplitude. It is by virtue of this method that enables wire 16 to become
shorted reliably by the acceleration, and helps start the subsequent
backward retraction of wire 16 quickly to obtain the distance between the
tip end of the wire and the base metal in a short period of time, when there
is an average distance of at least 1mm between the tip end of the wire and
the molten metal pool in the case of welding with a current range of 200Aor
larger having shorting occurring irregularly and frequency of the shorting
being about 80 times or less per minute.
With regard to the time required to end the welding, the embodied
method can complete the ending process by shorting only once as compared
to 100msec to 200msec needed to end the welding in the example of the
conventional control method described in the background art. The above
method can shorten the time necessary to end the welding to about 30msec
to 50msec, and it can hence reduce the production cycle time and improve
productivity.
What has been shown in this first exemplary embodiment is an
example, in which wire 16 is fed and accelerated periodically when the
welding end signal is input during the arcing period. However, wire feeding
speed controller 13 does not accelerate wire 16 until the shorting is opened
when the welding end signal is input while in the period of shorting. It is
acceptable for wire feeding speed controller 13 to feed and accelerate wire
16 periodically according to the predetermined cycle and amplitude and to
cause shorting of wire 16 with base metal 15 after the previous shorting is
opened. In the case of welding with a current range of 200A or smaller
having shorting occurring regularly and frequency of the shorting being as
high as about 80 to 100 times per minute, there is a short average distance
of about 1mm or less between the tip end of the wire and the molten metal
pool. Therefore, it rather results in a longer time needed to open the
shorting because wire 16 is thrust into the molten metal pool when wire 16
is accelerated to force the shorting upon receiving an input of the welding
end signal. Accordingly, the shorting can occur quickly enough even when
wire 16 is not accelerated, so that the subsequent backward retraction of
wire 16 can be started quickly to obtain the distance between the tip end of
the wire and the base metal in a short period of time by simply shorting
wire 16 without acceleration.
The first exemplary embodiment discussed here is an example, in
which feeding of wire 16 after the input of a welding end signal is carried
out periodically (there may be cases of less than one cycle) according to the
predetermined cycle (frequency) and amplitude. Instead of limiting the
feeding method as to be periodical, however, it is also appropriate to control
the feeding of wire 16 in such a manner that wire 16 is accelerated upon
input of the welding end signal to short it with base metal 15, and after the
shorting, wire 16 is retracted backward to open the shorting between wire
16 and base metal 15.
SECOND EXEMPLARY EMBODIMENT
In this second exemplary embodiment, like reference marks are used to
designate like structural components as those of the first exemplary
embodiment, and details of them will be omitted while description will
cover only different items. A main point of difference from the first
exemplary embodiment is that the wire feeding speed is decelerated at a
predetermined inclination from a point of time when a signal for turning off
the welding power output is input. Another point of difference is that wire
16 is retracted backward for a predetermined duration of time, starting
from a point when shorting occurs for the first time following the input of
the signal for turning off the welding power output, or a welding end signal,
so as to open the shorting and pull up wire 16 to end the welding.
There is also an alternative method as follows, instead of decelerating
the wire feeding speed at the predetermined inclination from the time when
the signal for turning off the welding power output is input. That is, the
wire feeding speed in the forward motion is kept unchanged rather than
decelerated, and the backward retraction of wire 16 is then started from the
point when the first shorting occurs following the input of the signal for
turning off the welding power output.
Fig. 3 is a graphic representation illustrating waveforms of wire
feeding speed, welding voltage and welding current according to the second
exemplary embodiment of this invention.
Time Tl shown in Fig. 3 is a time when the signal for turning off the
welding power output is input, and upon which a control process is
commenced for wire feeding speed Wf, welding current Aw and welding
voltage Vw in order to end the welding.
Wire feeding speed Wf is decelerated at the predetermined inclination
toward welding speed of 0 until the first shorting occurs. The wire feeding
speed is changed to begin the backward retraction when the first shorting
occurs at time T5 following the input of the signal for turning off the
welding power output. Wire 16 is then retracted backward at a constant
rate of predetermined wire retracting speed Wf2 for a predetermined
duration of time t3, and the retracting motion of wire 16 stopped thereafter
to ensure a sufficient distance (about 3mm to 8mm) between the tip end of
the wire and the base metal. Here, predetermined wire retracting speed
Wf2 is roughly lm/min to 20m/min, and predetermined retracting time t3 is
roughly 10msec to 30msec.
Since the shorting opens at time T6 during the backward retraction, a
predetermined value of constant welding current Al (about 30A to 100A) is
output for a predetermined duration of welding-current time t2 starting
from time T6 to melt wire 16 and control the shape of a globule formed at
the tip end of wire 16. Since the flow of welding current melts the tip end of
wire 16, it increases the distance between the tip end of the wire and the
base metal. This causes the distance between the tip end of the wire and
the base metal to become larger than 3mm to 8mm, which is the distance
provided by the backward retraction of wire 16.
In this second exemplary embodiment, the time to stop the wire feeding
speed is shown as not to coincide with the time to terminate the welding
power output, as such that the termination of the welding power output is
set later than the stop time of the wire feeding speed. However, they can be
set to coincide with each other, or the termination of the welding power
output may be set earlier than the other.
Furthermore, in the second exemplary embodiment, the welding
current is reduced sharply within a short period of time (about 2msec) from
time T6 so as to ease controlling of the shape of the tip end of wire 16, and a
duration of predetermined time t2 is timed beginning from time T6.
Referring now to Fig. 1, description is provided of an arc welding
apparatus of the consumable electrode type for carrying out arc-welding
control as discussed above. In Fig. 1, welding start dictator 12 sends a
welding end signal to output controller 11 and wire feeding speed controller
13 for turning off the welding power output. Wire feeding speed controller
13 decreases the wire feeding speed at the predetermined inclination of
deceleration toward welding speed of 0 until the first shorting occurs
following the input of the signal for turning off the welding power output.
In this embodiment here, the predetermined inclination of decelerating the
wire feeding speed is about 0.5m/sec2 to 2m/sec2.
When wire feeding speed controller 13 receives an input from short/arc
detector 10, indicating occurrence of the first shorting following the input of
the welding end signal, it starts the backward retracting motion at
predetermined wire retracting speed Wf2. It retracts wire 16 backward by
maintaining predetermined retracting speed Wf2 for the predetermined
duration of retracting time t3, and stops the retracting motion of wire 16.
Wire feeding speed controller 13 controls the wire feeding speed by sending
a signal for controlling the wire feeding speed to wire feeder 19. The
waveform for the wire feeding speed may be of any shape such as changing
it sharply to another speed like the wire retracting speed Wfl shown in Fig.
2, changing it like a half cycle of sinusoidal shape, or it may be changed to a
waveform of trapezoidal shape.
Wire feeding speed controller 13 is provided with storage device 21 and
wire feeding speed decision section 22. Here, storage device 21 stores
relational formulas or a table (data chart) that coordinate such parameters
as a setting current or an average value of wire feeding speed, a
predetermined inclination of decelerating the wire feeding speed following
the input of the signal for turning off the welding power output,
predetermined welding current time t2, backward retracting time t3 and
the like. Wire feeding speed decision section 22 decides such parameters as
an inclination of decelerating the wire feeding speed following input of a
welding end signal from storage device 21, predetermined welding current
time t2, backward retracting time t3 and the like according to a current
value set by welding condition setting section 23.
On the other hand, control of the welding power output given by the
welding current and welding voltage is carried out in the following manner.
Output controller 11 outputs a signal for controlling any of the welding
current and the welding voltage by using an appropriate parameter for a
shorting period, for instance if it is in the shorting period, corresponding to
the welding waveform parameter selected according to the welding current
and the welding voltage set by welding condition setting section 23. Or, it
outputs another signal for controlling any of the welding current and the
welding voltage by using an appropriate parameter for an arcing period if it
is in the arcing period. Any of these output signals is input to switching
element 4 to control the welding power output.
When welding start dictator 12 outputs to output controller 11 a
welding end signal for turning off the welding operation, and the first
shorting is opened, short/arc detector 10 outputs a signal of open-shorting.
Output controller 11 then operates in a manner to output a predetermined
value of constant welding current Al for a predetermined duration of
welding-current time t2 after opening of the shorting in order to control the
size of the tip end of wire 16.
As discussed, the arc welding apparatus in the second exemplary
embodiment of this invention is the consumable electrode type used for
welding by generating arc 17 between welding wire 16 serving as a
consumable electrode and base metal 15 as an object to be welded. The arc
welding apparatus comprises welding condition setting section 23,
switching element 4, welding voltage detector 9, welding start dictator 12,
short/arc detector 10, output controller 11, storage device 21, wire feeding
speed decision section 22 and wire feeding speed controller 13. In this arc
welding apparatus, wire feeding speed controller 13 continues to feed wire
16 forward at the same feeding speed until sorting between wire 16 and
base metal 15 occurs for the first time after the welding end signal is input
while arc 17 is being generated. Or, it decelerates the feeding speed of wire
16 at a predetermined rate from the previous forward feeding speed. When
the first shorting occurs after the input of the welding end signal, wire
feeding speed controller 13 starts backward retraction of wire 16 at a
predetermined retracting speed for a predetermined duration of time.
After that, wire feeding speed controller 13 stops the feeding/retracting
motion of wire 16. Output controller 11 terminates the welding power
output after supplying the welding current of a predetermined amount for a
predetermined duration of welding time starting from the point of time
when opening of the shorting occurs during the retracting motion of wire
16.
These operations can ensure a shape of proper size at the tip end of
wire 16 without variations, and a sufficient distance between the tip end of
wire 16 and the base metal 15 to prevent them from becoming welded
together, thereby avoiding interruption of the manufacturing operation.
With regard to the time required to end the welding, the embodied method
can complete the ending process by shorting only once as compared to
100msec to 200msec needed to end the welding in the example of the
conventional control method described in the background art. The above
method can shorten the time necessary to end the welding to about 30msec
to 50msec, and it can hence reduce the production cycle time and improve
productivity.
Although the method discussed in this second exemplary embodiment
is of the case, in which the welding end signal is input during the period of
arcing, it is also appropriate to let the backward retraction of wire 16 start
at the time of receiving the welding end signal if it is input during the
shorting period. Accordingly, it becomes possible to ensure the distance
between the tip end of the wire and the base metal in a short period of time
because the backward retraction is started immediately after input of the
signal during the shorting period.
INDUSTRIAL APPLICABILITY
According to the present invention, the method and the apparatus are
useful for industrial applications for arc welding with a welding wire of
consumable electrode being fed continuously.
Reference Marks in the Drawings
1 Mains power source
2 Main power transformer
3 Primary rectifier element
4 Switching element
5 Reactor
6 Secondary rectifier element
8 Welding current detector
9 Welding voltage detector
10 Short/arc detector
11 Output controller
12 Welding start dictator
13 Wire feeding speed controller
14 Welding power unit
15 Base metal
16 Wire
17 Arc
18 Torch
19 Wire feeder
20 Tip
21 Storage device
22 Wire feeding speed decision section
23 Welding condition setting section
we claim:

1. An arc welding method comprising the steps of:
accelerating a feeding speed of a welding wire to cause shorting
between the welding wire and a base metal when a welding end signal is
input during a period of arcing,"
retracting the welding wire backward thereafter until a wire retracting
speed reaches a predetermined rate!
controlling the wire retracting speed to maintain it constant for a
predetermined duration of time! then
stopping the backward retraction of the welding wire; and then
terminating a welding power output after supplying a predetermined
amount of welding current for a predetermined duration of welding time
starting from a point of time when opening of the shorting occurs during the
backward retraction of the welding wire.
2. The arc welding method of claim 1, wherein the acceleration of the
welding wire is carried out according to predetermined cycle and amplitude,
and the backward retraction of the welding wire is also carried out
according to the predetermined cycle and amplitude.
3. The arc welding method of any of claim 1 or claim 2, wherein the
acceleration of the welding wire is halted until the shorting is opened when
the welding end signal is input during a period of the shorting, and the
acceleration of the welding wire is started to cauae the shorting after the
previous shorting is opened.
4. An arc welding method comprising the steps of:
continuing forward feeding of a welding wi>-e by keeping a forward
feeding speed unchanged from a feeding speed maintained before a welding
end signal is input, or decreasing the forward feeding speed of the welding
wire at a predetermined rate of deceleration from the feeding speed
maintained before the welding end signal is input, until an initial shorting
occurs between the welding wire and a base metal after the welding end
signal is input during a period of arcing; then
starting backward retraction of the welding wire upon occurrence of
the shorting, and continuing the backward retraction at a predetermined
retracting speed for a predetermined duration of time!
stopping the backward retraction of the welding wire; and then
terminating a welding power output after supplying a predetermined
amount of welding current for a predetermined duration of welding time
starting from a point of time when opening of the shorting occurs during the
backward retraction of the welding wire.
5. The arc welding method of claim 4, wherein the backward retraction
of the welding wire is started at a time of receiving the welding end signal
when the welding end signal is input during a period of the shorting.
6. An arc welding apparatus of consumable electrode type used for
welding by generating arc between a welding wire serving as a consumable
electrode and a base metal as an object to be welded, the apparatus
comprising:
a welding condition setting section for setting a welding condition;
a switching element for regulating a welding power output;
a welding voltage detector for detecting a welding voltage;
a welding start dictator for giving a comma: id of starting or stopping
the welding power output;
a short/arc detector for detecting whether a v/elding condition between
the welding wire and the base metal is in a short mode or in an arcing mode
according to an output of the welding voltage detector!
an output controller for controlling the switching element in a manner
to produce any of predetermined current waveform and voltage waveform
according to a given current set in the welding condition setting section and
an output of the short/arc detector;
a storage device for storing the set current, a frequency of wire feeding
speed, an amplitude of the wire feeding speed and an average value of the
wire feeding speed in a coordinated fashion;
a wire feeding speed decision section for deciding the average wire
feeding speed, the frequency and the amplitude retrieved from the storage
device based on the set current; and
a wire feeding speed controller for receiving an output of the short/arc
detector and an output of the wire feeding speed decision section, and
controlling the wire feeding speed in a manner to periodically repeat
forward and backward, wherein
the wire feeding speed controller accelerates feeding of the welding
wire according to predetermined cycle and amplitude to make a short
between the welding wire and the base metal when a welding end signal is
input during a period of the arcing, then retracts the welding wire
backward according to the predetermined cycle and amplitude until a wire
retracting speed reaches a predetermined rate, continues the backward
retraction thereafter by controlling the wire retracting speed constant at
the predetermined rate for a predetermined duration of time, and then
stops the retraction of the welding wire, and
the output controller terminates the we]ding power output after
supplying a predetermined amount of constant welding current for a
predetermined duration of time starting from a point of time when opening
of shorting occurs during the backward retractioa of the welding wire.
7. The arc welding apparatus of claim 6, wherein the wire feeding
speed controller refrains from accelerating the welding wire until the
shorting is opened when the welding end signal is input during a period of
the shorting, and accelerates the welding wire according to predetermined
cycle and amplitude after the shorting is opened, to cause the shorting
between the welding wire and the base metal.
8. An arc welding apparatus of consumable electrode type used for
welding by generating arc between a welding wire serving as a consumable
electrode and a base metal as an object to be welded, the apparatus
comprising:
a welding condition setting section for setting a welding condition;
a switching element for regulating a welding power output;
a welding voltage detector for detecting a welding voltage!
a welding start dictator for giving a command of starting or stopping
the welding power output;
a short/arc detector for detecting whether a welding condition between
the welding wire and the base metal is in a short mode or in an arcing mode
according to an output of the welding voltage detector;
an output controller for controlling the switching element in a manner
to produce any of predetermined current waveform and voltage waveform
according to a given current set in the welding condition setting section and
an output of the short/arc detector!
a storage device for storing the set current and a wire feeding speed of
the welding wire used after a welding end signal is input in a coordinated
fashion;
a wire feeding speed decision section for deciding the wire feeding
speed retrieved from the storage device based on the set current; and
a wire feeding speed controller for receiving an output of the short/arc
detector and an output of the wire feeding speed decision section, and
controlling the wire feeding speed, wherein
the wire feeding speed controller continues forward feeding of the
welding wire by keeping a forward feeding speed unchanged from a feeding
speed maintained before the welding end signal is input, or decreasing the
forward feeding speed of the welding wire at a predetermined rate of
deceleration from the feeding speed maintained before the welding end
signal is input, until an initial shorting occurs between the welding wire
and the base metal after the welding end signal is input during a period of
the arcing,' then
starting backward retraction of the welding wire upon occurrence of
the shorting, and continuing the backward retraction at a predetermined
retracting speed for a predetermined duration of time; and
the output controller terminates the welding power output after
supplying a predetermined amount of constant welding current for a
predetermined duration of time starting from a point of time when opening
of shorting occurs during the backward retraction of the welding wire.
9. The arc welding apparatus of claim 8, wherein the wire feeding
speed controller starts the backward retraction of the welding wire upon
receiving the welding end signal when the welding end signal is input
during a period of the shorting.

An arc welding method comprising the steps of accelerating a feeding
speed of a welding wire to cause shorting between the welding wire and a
base metal when a welding end signal is input during a period of arcing,
retracting the welding wire backward thereafter until a wire retracting
speed reaches a predetermined rate, controlling the wire retracting speed
constant at this speed for a predetermined duration of time, then stopping
the backward retraction of the welding wire, and then terminating a
welding power output after supplying a predetermined amount of welding
current for a predetermined duration of time starting from a time when
opening of the shorting occurs during the backward retraction of the
welding wire.